The present invention relates to an antenna element and, in particular, relates to an antenna element suitable for receiving a GPS signal from a GPS satellite.
As is well known in this technical field, various kinds of antennas are mounted on a vehicle. There is an antenna for GPS (Global Positioning System) as one of such antennas.
The GPS is a positioning system using a satellite. The GPS is configured to receive radio waves (GPS signals) from four or more satellites among twenty four satellites (hereinafter referred to as GPS satellites) orbiting the earth. The GPS is capable to calculate the position and altitude (on a map) of a movable body with a high accuracy based on the theory of the triangular survey using positional relations and time differences between the movable body and the GPS satellites obtained by the received radio waves (GPS signals).
In recent years, the GPS is utilized and widely spread. For example, the GPS is used for a vehicle navigation system for detecting the position of a vehicle in a running state. The vehicle navigation device includes a GPS antenna for receiving the GPS signals, a processor for processing the GPS signals received by the GPS antenna to thereby detect the current position of the vehicle, and a display for displaying the position detected by the processor on a map. A flat antenna such as a patch antenna is used as the GPS antenna.
The patch antenna disclosed in Japanese Patent Publication No. 2008-66979A includes a dielectric substrate, a patch antenna electrode, a ground electrode and a feeding pin. The dielectric substrate has a top face and a bottom face opposing each other. The dielectric substrate is provided with a through hole penetrating from the top face to the bottom face at a feeding point. The patch antenna electrode is formed by a conductive material and provided on the top face of the dielectric substrate. The ground electrode is formed by a conductive material and provided on the bottom face of the dielectric substrate. The ground electrode has an opening which is substantially concentric with the through hole and the diameter of which is larger than the diameter of the through hole. The feeding pin has a first end and a second end. The first end of the feeding pin is coupled to the patch antenna electrode at the feeding point. The second end of the feeding pin is led to the bottom face side of the dielectric substrate through the opening. The feeding point is provided at a position away from the center of the patch antenna electrode.
A portable navigation device is known. The GPS antenna is required to be attached in the portable navigation device. There are two ways for attaching the GPS antenna to the portable navigation device. The first way is that the GPS antenna is attached to the exterior of the portable navigation device. The second way is that the GPS antenna is provided within the portable navigation device. There are two methods the correspond to the first way. The first method is that an antenna housing accommodating the GPS antenna is provided on an upper portion of the portable navigation device. The second method is that the antenna housing is attached at an arbitrary angle. On the other hand, in the second way, the GPS antenna is disposed on a circuit board accommodated within the portable navigation device.
An antenna device disclosed in Japanese Patent Publication No. 2006-261941 A can realize at least one of a directionality control and a multi-frequency adaptation. The antenna device includes a base plate, a dielectric member formed on one major face of the base plate, a substantially rectangular feeding element formed on a top face of the dielectric member which is opposite to a face of the dielectric member opposing the base plate, a substantially rectangular parasitic element disposed symmetrically to the feeding element along an electric field face and a magnetic field face, and a switch formed at least at one of regions near four apexes of the parasitic element and short-circuiting the feeding element and the base plate.
With reference to FIGS. 1 through 5, a conventional patch antenna 10 will be explained. In FIGS. 1 to 3, the forward and backward direction (depth direction) is represented by an X-direction, the left and right direction (width direction) is represented by a Y-direction, and the elevational direction (height direction, thickness direction) is represented by a Z-direction.
The patch element 10 is constituted by a dielectric substrate 12 having a substantially rectangular parallelepiped shape, a patch antenna electrode 14, a ground electrode 16 and a feeding pin 18 having a rivet shape.
The dielectric substrate 12 is formed by ceramic material having a high permittivity (for example, a relative permittivity ∈r is 20) such as barium titanate. The dielectric substrate 12 has a top face 12u and a bottom face 12d opposing to each other in the Z-direction, and side faces 12s. The corners of the side faces 12s of the dielectric substrate 12 are chamfered. The dielectric substrate 12 is provided with a through hole 12a which penetrates from the top face 12u to the bottom face 12d. 
In the example shown in the drawings, the dielectric substrate 12 is arranged to have a size that the length in the X-direction is 25 mm, a length in the Y-direction is 25 mm, and a length in the Z-direction is 4 mm.
The patch antenna electrode 14 is formed by conductive material and provided at the center portion of the top face 12u of the dielectric substrate 12. The patch antenna electrode 14 has a rectangular shape and a size wherein a length in the X-direction is 12.3 mm and a length in the Y-direction is 12.5 mm. The patch antenna electrode 14 is formed by a silver pattern printing, for example.
As shown in FIG. 2D, the ground electrode 16 is formed by conductive material and provided at the bottom face 12d of the dielectric substrate 12. The ground electrode 16 has an opening 16a which is substantially concentric with the through hole 12a and the diameter of which is larger than the diameter of the through hole 12a. 
A feeding point 15 is provided at the position shifted in the X-direction and the Y-direction from the center of the patch antenna electrode 14. An upper end portion 18a of the feeding pin 18 is coupled to the feeding point 15. A lower end portion 18b of the pin 18 is lead to a lower side of the ground electrode 16 through the through hole 12a and the ground opening portion 16a. 
A solder is used as the feeding point 15. Thus, the feeding point 15 has a convex shape protruded from a major face of the patch antenna electrode 14.
The feeding pin 18 shown in the drawing includes a rivet pin having a head 181 provided at the upper end portion 18a and a rod-shaped body 182 extending to a lower end portion 18b of the feeding pin 18 from the upper end portion 18a. The head 181 of the feeding pin 18 is joined to the patch antenna electrode 14 by soldering in a state that the head 181 of the feeding pin 18 protrudes from the major face of the patch antenna electrode 14.
The antenna element 10 is incorporated or accommodated in a portable navigation device (PND) 80 as shown in FIG. 4, when the antenna element 10 can be used as the GPS antenna.
The portable navigation device (PND) 80 shown in FIG. 4 includes a casing 82 and a display 84 provided on the front face of the casing 82. In this case, the antenna element 10 is mounted on a circuit board (described later) accommodated within the portable navigation device 80.
As shown in FIG. 5, such a portable navigation device 80 can also be used as a vehicle navigation device by disposing vertically on the dashboard within a vehicle. In this case, the circuit board 86 of the portable navigation device 80 is also disposed in a vertical attitude. Thus, since the antenna element 10 used as the GPS antenna is also mounted on the major face of the circuit board 86, the normal line of the top face 12u of the dielectric substrate 12 is directed to the horizontal direction with respect to the GPS satellites 70 existing in the zenith direction, that is, the front direction of the vehicle, for example.
As shown in FIG. 5, in the conventional patch antenna element 10, the main beam is always directed in the vertical direction (normal direction) A with respect to the top face 12u of the dielectric substrate 12. Thus, in the conventional patch antenna 10, it becomes difficult to efficiently receive the GPS signals from the satellites 70.
The Japanese Patent Publication No. 2006-261941 A merely discloses an antenna device which can realize at least one of directionality control and the multi-frequency adaptation and does not disclose or suggest disposing the antenna device within the portable navigation device or a problem caused in this case.